First birds don't die from bread. If so then all of the parks in america would have a pile of ducks layin everywhere and bread is fed to common birds all of the time. I think stuff like alcaseltzer kills them because they can't expell the gas quick enough or it might have something to do with their gullet. Most of the fish foods people feed (cichlid gold, cichlid staple, shrimp pellets, algae wafers, and all dehydrated foods) absorb liquid and expand. Why would that be different than bread? Second the uncooked flour on the bottom of bread is put in the cooking pans so they don't stick, not the cooling racks. Atleast thats how we do it at our bakery. The flour used to not stick is pure flour, it has no yeast or sugar in it or that would melt and cause the bread to burn. Thirdly, have you looked at ingredients in Cichlid staple and shrimp pellets and such. They have stuff like Wheat flour, corn gluten meal, rice bran, and multiple types of yeast. So, all in all I believe bread is not more harmfull than your store bought fish foods.